Fix link error for test_radixtree module on Windows
Add back "link_with" directive, similar to the one removed by
1f1d73a8b,
but only for Windows, but use the "_shlib" variation.
Diagnosis by Masahiko Sawada, proposed fix adjusted and tested by me
Per buildfarm members drongo and fairywren
Discussion: https://postgr.es/m/CAD21AoAMm1mQd%3Dw4PrfrKK%3DOMP8j8%3D7ntJRPF8%2B%3D10iUuvwiCA%40mail.gmail.com